The general aims of this study are to evaluate the interaction of temperament and feeding in infants to determine its impact on infant weight gain. The problem of pediatric obesity is cause for serious concern, as some 6 million American children are fat enough to signal a real public health problem. The health implications are sobering, as diabetes, fatty liver, and obstructive sleep apnea in childhood may foreshadow coronary heart disease or even cancer in adulthood. In recent years, rates of overweight in infancy have increased across all ethnicities, exceeding those of preschool-aged children. While persistent overfeeding or low physical activity might seem to be the explanation for excessive early weight gain, studies of energy intake and expenditure in infancy have reported conflicting results. Because low-income, minority children who are formula-fed appear to be a population at particular risk for obesity, yet little investigated in infancy, this study will enroll an urban sample of 50 black and 50 Hispanic mother-infant dyads. Mothers will be enrolled in the study a day after giving birth, with some maternal and infant data collected at that time, and when the infants are approximately 3-, 6-, and 12-months or age. Data collected will consist of health records, maternal reports of feeding and ratings of infant irritability, mechanical measures of motor activity, and observations of a feeding. The specific aims of the proposed project are to assess maternal feeding in response to infant temperament; to determine how infant temperament contributes to infant weight gain; and to evaluate the independent impact of activity, irritability, and feeding patterns on infant weight gain using a multivariate model.